Availability means resistance to failure. In particular, in computer systems in which instantaneous interruption is not permitted, such as computer systems used in plant control and aircraft control, various measures are taken in order to improve the availability of the computer systems for continuous operation.
Technologies to make processors or servers redundant are known as the technologies to improve the availability of the computer systems. For example, the following technology is disclosed in a certain document. Specifically, each arithmetic processing unit determines the state of the own arithmetic processing unit using arithmetic operations and transmits state data indicating the state of the own arithmetic processing unit to multiple determination units on a certain cycle. Each of the determination units selects normal arithmetic processing units based on the state data and notifies a control unit of the result of the selection. The control unit extracts a normal arithmetic processing unit from the result of the selection received from each determination unit based on a majority rule.
In this technology, each arithmetic processing unit determines the state of the own arithmetic processing unit, each determination unit selects the normal arithmetic processing units, and the control unit extracts the normal arithmetic processing unit based on the majority rule. Accordingly, it may take a time to finally extract the normal arithmetic processing unit and no consideration is taken for the time.
For example, an example of the related art is disclosed in Japanese Laid-open Patent Publication No. 2013-239034.